Carbon burn off and heating element damage - WarmGlass.com

Carbon burn off and heating element damage

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Alexis Dinno
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Joined: Sun Dec 13, 2009 9:35 pm

Carbon burn off and heating element damage

Postby Alexis Dinno » Sun Aug 03, 2014 4:14 pm

Hey good people,

I have caught warnings hither and thither about careful ventilation of electric kilns with coil-type heating elements when burning off carbon, and perhaps other substances (e.g. CMC or other binders, etc.). I believe I have also heard it expressed also that creating an unenclosed reducing atmosphere in the kiln—say, because you wanna go cray-cray with certain ceramic glaze styles of chemistry—is quite bad for the heating elements. That's cool and all, and I try and behave nicely to my kiln, and worry about long term lifespan of my heating elements. Two questions, though:

Do these cautions apply to heating elements that are embedded within a ceramic lid? (I assume so, but thought I would ask).

I was talking to an engineer friend about glass and kiln work, and he was puzzled by the process whereby a reducing atmosphere harms the heating elements. Can someone explain the chemistry and physics behind it?

Thanks!

Bert Weiss
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Re: Carbon burn off and heating element damage

Postby Bert Weiss » Mon Aug 04, 2014 10:27 am

I'll await a comprehensive answer. What I can say is that small amounts of organic material, like some CMC do not come close to consuming all the oxygen and creating a reduction atmosphere.

My common sense tells me that elements in quartz tubes or embedded in fiber would not be significantly effected by the atmosphere. Tubes that go through the walls certainly isolate their atmosphere from the hot kiln.
Bert

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charlie
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Re: Carbon burn off and heating element damage

Postby charlie » Mon Aug 04, 2014 11:05 am

in a reducing atmosphere, the glazes want oxygen. if there's little to none in the air, then it's going to come from somewhere. there's an oxide on the elements, which then gives up it's O to get pulled into the glaze. the oxide protects the outside of the element, and if it's not there or thinner, it doesn't do this job.

rosanna gusler
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Re: Carbon burn off and heating element damage

Postby rosanna gusler » Mon Aug 04, 2014 11:54 am

like they said there is an oxide coating formed on the element the first time it is fired. it stays there untill there is a reducing atmosphere in the kiln. then the next time the kiln is fired the oxide forms again. this can eventually wear the element thin. if you want to do some reducing stuff , you can use a saggar to contain that atmosphere. i burn out a lot of organics in my kilns and always vent to 1100f or so. if i use the skutt kiln to burn labels off of bottles i find that i need to fire the kiln empty to 100f or so above my usual top process temp. this burns off whatever has remained in the kiln. if i do not do that i will get amazing crystal looking devit on the firing after the bottle cleaning one. R.
artist, owner of wanchese art studio, marine finisher

Alexis Dinno
Posts: 56
Joined: Sun Dec 13, 2009 9:35 pm

Re: Carbon burn off and heating element damage

Postby Alexis Dinno » Mon Aug 04, 2014 3:11 pm

Thank you all so much.

Bert: yes, I wasn't intending to imply that binders consume all oxygen, or that they produce the kinds of reducing environments yielded by adding wood or... I dunno, a bag of m&ms to the kiln interior.

So if I understand the responses, the heating element damage (for coil-type elements) caused by creating reducing atmospheres is an induced mechanical weakening and/or wearing of the coils due to cycles of metal oxidation and reduction?

Cheerio


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